Fuel injection pumps



Dec. 1, 1959 J. N. MORRIS 2,915,014

FUEL INJECTION PUMPS Filed Feb. 23, 1956 FIG. I. f

INVENTOR. JOHN NEVILLE MORRIS.

m u4mj nam i ATTORNEYS.

United States Patent v FUEL INJECTION PUlVlPS John N. Morris,Birmingham, England, assignor to The S.U. Carburetter Co. Ltd.',Birmingham, England, a British company i I ApplicationFehruary 23, 1956,Serial No. 567,395

- Claims priority, application Great Britain liebruary24, 195'5 8Claims. (Cl. 103-38) This invention relates to a fuel injection pump forinternal combustion engines. More particularly, it is directed to a pumpof the type having adjustable means controlling the delivery of one ormore pump members, and a displaceable pressure responsive member forcontrolling the adjustable means disposed in' a housing and forming withsaid housing a first and asecond pressure 7 chamber on respective sidesof said displaceable member.

In order to supply the liquid fuel to spark-ignition engines of the typeemployed in automatic vehicles or certain stationary installations, thefuel injection pump must be capable of responding rapidly to suddenchanges in the position of the engine accelerator control. Fuelinjection pumps have been employed for some time in connection withaircraft engines; however, since the speed with which they follow themovement of the throttle is not too important the emphasis has beenplaced upon steady-state metering accuracy. The present invention is,directed to a construction ofan injection pump which isparticularlyadapted for use where rapid accommodation to sudden changes in fueldemand is required. For convenience in explanation, the invention willbe described with reference to one specific type of injection pump;however, as will appear from the description, the invention isapplicable to other pumps of the general character outlined in theintroductory paragraph above.

In accordance with the invention a fuel injection pump having such basicelements as above enumerated is further provided with means forsupplying a-substantially unrestricted flow of fluid under pressure tothefirst pressure chamber, a servovalve-controlled passageinterconnecting the first and second pressure chambers, a servo-valvetherefor, and a restricted passage for venting the second pressurechamber. The opening in the valve-open positon of the servo-valve ischosen relative to the size of the restricted passage so as to permit arapid build-up of fluid pressure in the second pressure chamber when theservo-valve is in its wide open position.- This enables the pump toshift rapidly in a first direction. In orderto enable the pump to shiftrapidly in the reverse direction, an auxiliary venting means for thesecond pressure chamber is provided. This includes a ventpassage of asize related to the restricted passage and to the size of the secondpressure chamber such as to decrease rapidly the pressure in the secondpressure chamber 'whenunrestricted. The servo-valve is operativelyassociated with the last mentioned vent passage for restricting the flowof fluid therethrough except when in the servo-valve-closed position.

As a further feature of the invention the functions of the restrictedpassage and of the auxiliary vent passage inay be combined in a singlepassage controlled by the servo-valve. Now, however, the servo-valve isar ranged to cause restricted flow through the passage during normalsteady-state operation and unrestricted flow when the servo-valve is inits valve-closed position.

' A better understanding of the invention will be had 2,915,014 PatentedDec. 1, 1959 from a reading of the following detailed description withreference tothe accompanying drawings in which:

Fig. 1 is an elevational view partly in section showing a fuel injectionpump embodying the present invention;

Fig. 2 is a fragmentary elevational viewvshowing the servo-valve and thebifurcated lever for coupling the input signal thereto; and 1 p v r Fig.3 is a sectional view taken on line 33 in Fig. 2.

Referring now to the drawings, the fuel injection pump is providedwith acast housing 10 having a capsule pressure chamber 12 and an operatingchamber 14. A drive shaft 16 passes through the chamber 14 and has itsupper end, which is not shown in the drawing, operatively connected to adistributing valve arrangementfor sequentially connecting the pumpcylinders, one of which is shown at 18, to the fuel supply and to theinjection nozzles for the engine. The other end of the drive shaft isarranged to be driven by the engine in a suitable manner. The cylinder18 along with a suitable number of further cylinders, not shown, arepositionedin the I form of a circle in a cylinder block 20. Each of thecylinders is provided with a pump member in the form of a plunger 22 ofwhich two are visible in the drawing. The jplungers 22 bear against awobble-plate 24 which is mounted upon acombined skew shaft andservo-piston unit 26,. The unit 26 is slidably mounted upon the shaft 16and keyed thereby by a key 28 for driven rotation therewith. The unit 26is provided with a cylindrical apron 30 making a sliding fit in thecylindrical portion 32 of the housing .10. The apron 30 along with theweb portion 34 of the unit 26 forms a displaceable pressure. responsivemember within the aforementioned cylindrical portion 32 The wobble-plate24 has its peripheral region provided with abearing surface whichengages a complementary surfacein the housing 10. This surface may begenerally spherical in nature. As the com-. bined skew shaft andservo-piston unit 26 moves longitudinally along the drive shaft 16the'skew portion 'of the unit 26 will displace the center of thewobble-plate 24 thereby increasing or decreasing its tilt orinclination. In: a known manner rotation of the skew shaft will causethe wobble-plate to reciprocate the pump members 2'2. Asshown in thedrawing, the stroke of the pump members will be a maximumwhen the unit26 occupies its extreme upward position and will be a minimum when theunit 26 occupies its extreme lowermost position.

Provision is made for connecting a source of fiuiduuder pressure to thehousing 10 through the large port 36 for establishing a substantiallyunrestricted flow thereof. The pressure fluid might conveniently bethelubricating oil employed in the'engine. The fluid will fill up theportion of the chamber 14.above the unit 26 (afirst; pressure chamberand pass into a servo-valvecontrolled pas sage 38 formed in the driveshaft 16 by way of the ports 40. It is noted that theports 40 arelocated at a point on the drive shaft 16 above theupper limit ofmovement of the servo-piston unit 26 ;A further group of comparativelylarge ports 42 are located inthe walls of the drive shaft 16 incommunication with the passage 38 in the lower portion of the chamber1,4.ata point well below the'lower limit of travel of the servoepistonunit 26. A servo-valve in the form of a cylindrical sleeve mem ber 44 ismounted for :sliding movement longitudinally uponthe drive shaft 16. -Asshown in the drawing, the valve 44 isprovidedpwith a land area 46 whichcooperates with the portsfl42 toprovide a variable obstruction ther-er,

- for dependent upon the relative positionv of the servo:

valve. As long as-the ports 42, are not completelyv obstructed orclosedthe pressurefluid will leave the passage,

50 formed in the walls thereof. This fluid will now commence to fill upthe portion of the chamber 14 located below the servo-piston 26 (asecond pressure chamber).

A vent passage 52 is formed within the drive shaft 16 and communicatesthrough a lateral passage 54' with the exterior of the housing 10. Theother end of the passage 52 communicates with a plurality of vent portand passage means 56 and 58 which are located in the shaft 16 within thelower portion of chamber 14. The vent port and passage means 56 islocated with respect to the servo-valve such that the lower portion 60thereof completely obstructs the port means 56 for all positions of theservovalve except that position wherein the land area 46 completelyobstructs or closes off the ports 42, i.e. for all positions other thanthe servo-valve-closed position. The reason for this will be describedbelow. The other vent port and passage means 58 is located at a pointwhich is always unobstructed by the servo-valve and forms with thepassages 52 and 54 a permanent restricted passage for venting theaforementioned second pressure chambet in the lower portion of chamber14. The ports 42 as well as the clearance or groove 48 and ports 50 inthe servo-valve should be of such size and proportionthat the opening inthe valve-open position of the servo-valve relative to the size of therestricted passage 58 will permit a rapid build-up of pressure in thesecond pressure chamber below the servo-piston 26.

A helical compression spring 62 surrounds the drive shaft 16 and isdisposed between the web 34 of the servopiston 26 and the upper face ofthe servo-valve 44. This serves as a feedback coupling between theservo-piston and the servo-valve. A thrust race 64 is provided betweenthe spring 62 and the upper face of the valve 44. The spring 62 urgesthe valve 44 downwardly against the bifurcated ends 66 of an articulablelink or see-saw lever 68 which straddles the drive shaft 16. As seen inFigs. 2 and 3 the ends 66 of the lever 68 are provided with taperedbearing surfaces 70 engaging V-notches 72 formed in the lower edge ofthe servo-valve 44. This prevents rotation of the servo-valve and at thesame time applies the controlling force thereto. The other end of thelever 68 is acted upon by a thrust pin 74 which in turn is engaged by asecond thrust pin 76 fixed to one face of a pressure responsive device78 situated in the chamber 12. The device 78 may take the form ofasealed multicapsule stack. The chamber 12 is provided with a port 80for connection with the air induction manifold of the engine. Theopposite face of the device 78 is positioned centrally by an adjustableabutment pin 82.

So long as the operating conditions of the engine remain unchanged(i.e., while the induction manifold pressure applied to the capsule unitin the chamber 12 remains constant), the mechanism described above is ina stable state. This arises from the circumstance that, under theconjoint influences of the control spring 62 and the load transmitted bythe linkwork 68, 74 and 76 from the capsuleunit 78, the servo-valve 44assumes a position in which its land area 46 so regulates the effluxof'fiuid through the outlet ports 42 that, in conjunction with therestricted provision for escape of fluid from the second pressurechamber, the differential fluid pressure acting on the servo-piston unit26 exactly balances the load exerted by the control spring 62.Consequently, any given load exerted upon the servo-valve 44 by thecapsule unit 78 and its associated linkwork is necessarily exactlycounterbalanced by the load exerted by'the control spring 62, and,therefore, corresponds to a particular length of that spring and hence adefinite position of the combined skew shaft and servo-piston'unit 26.Thus, any given value of the induction manifold pressure results in acorresponding. stroke being performed by the fuelpumping plungers 22.

Letit be assumed that the pump is in a stable fuelmetering conditionwith a relatively low pressure obtaining in the chamber 12; which, ofcourse, corresponds i to the engine either idling or being on light load(that is to say, when the throttle valve admitting air into theinduction manifold is partially shut). :If now the throttle is abruptlyopened, the induction manifold pressure rises very rapidly, for exampleto atmospheric pressure or to some pressure intermediate. between thelow pressure previously existing and atmospheric pressure. The capsuleunit 78 has a relatively low elasticity and, therefore, this suddenincrease in its ambient pressure not only has the effect of diminishingmomentarily the thrust exerted by the capsule unit on its associatedlinkwork, but also enables the capsule unit to undergo a substantialcontraction. This permits the servo-valve 44 momentarily to slide underthe influence of the control spring 62, it being borne in mind that atthe instant of opening the throttle and consequently applying the suddenincrease in pressure to the capsule unit 78 the pump was operating at arelatively small stroke; that is to say, the control spring 62 wassubstantially compressed and exerting a relatively large load upon theservo-valve.

The momentary downward displacement of the servovalve 44 brings about amomentary large increase in the effective opening of the associatedoutlet ports 42, and thus permits high-pressure fluid from the passage38 in the drive shaft 16 to flow through these portsat' a high rate intothe relatively lower-pressure region constituted by the second pressurechamber. This momentary high flowof fluid temporarily raises the fluidpressure behind the servo-piston unit 26 to such a value that, acting onthe rear face of the servo-piston and thereby assisting the controlspring, the latter is enabled to expand and rapidly move theservo-piston unit. A condition of stability is eventually established,with the control spring '62 now more distended and the servo-piston unit26 having moved to a position corresponding to a greater stroke of thefuel-pumping plungers 22. The load exerted by the control spring on theservo-valve eventually exactly counterbalanccs the new load exerted bythe capsule unit 78.

It will be appreciated from the foregoing description that the provisionof outlet ports 42 in the drive shaft which are of substantial depth andperipheral extent, taken in conjunction with the relatively low springrate of'the capsule unit 78, permits the stroke-varying mechanism torespond very rapidly to an abrupt increase in the'induction manifoldpressure.

Now consider the operation of the device when the throttle is suddenlyclosed or partially closed from a formerly open position. For thispurpose assume, initially, that the port means 56 has been omitted. TheConcomitant sudden reduction in the induction manifold pressure causesthe capsule unit 78 momentarily to distend, it being free to do so sinceat the instant of the change of pressure in the induction manifold thecontrol spring was relatively distended, corresponding to a substantialdisplacement of the servo-piston unit towards the full-stroke position.The control spring 62 was, therefore, at the instant underconsideration, exerting a relatively small load upon the servo-valve.Now the sudden distension of the capsule unit momentarily causes theservo-valve to be moved by the lever 68 against the control spring 62,and this movement results in the valve completely closing the outletports 42 in the drive shaft, thus precluding temporarily any furtherflow of oil from one side of the servo-piston unit to the other. Underthe action of the high-pressure fluid on its front face, theservo-piston unit now proceeds to move towards the position at which theamplitude of the wobble-plate 24 is diminished, forcing the fluid out ofthe second pressure chamber by way of the restricted vent passagereferred to earlier. This the servo-piston unit is free to do since thefluid behind it is momentarily no longer being replenished as it isnormally by the passage of fluid past the \land area 46 on theservo-valve 44. The rate at which this movement of the servo-piston unittakes place is, however, limited by the necessarily relatively srnallsize of the vent passage by which fluid can escapefrom the secondpressure chamber. The vent passage has to be relatively small in orderto limit the amount of fluid supplied by way of the relatively largeport 36 to the front face of the servo-piston unit. In consequence theresponse of the mechanism to a sudden closure of the throttle is verysluggish and a considerable interval of time may elapse before themechanism has readjusted itself to the new pressure obtaining in theinduction manifold. During this interval the fuel delivered to theengine is excessive, and misfiring and temporarily excessive fuelconsumption result.

Now consider the effect of the port means 56 which, under normal steadymetering conditions (i.e. when the land area 46 of theservo-valve 44 isvery close to its shut off position with respect to the associated ports42), are just covered by the valve 44 and are thus inoperative as aleakage or vent path. During the momentary phase when the capsule unit78 is substantially expanded temporarily, and consequently the valve 44has been moved against the spring 62 and has shut off the associatedports 42, the vent port and passage means 56 becomes exposed and thussaid means 56 incombination with passages 52 and 54 serves as anadditional or auxiliary venting means for second chamber, 14 whichauxiliary means is in parallel with the permanently opened passage ofrelatively small size previously mentioned, for the fluid to escape fromthe lower portion of chamber 14 to the exterior of the housing 10.

As will be appreciated from the above description, the effect oftheprovision of the auxiliary venting passage is momentarily to increasethe rate of fluid venting or spillage from the low pressure side of theservo-piston unit 26, thus increasing the speed at which theservopis-ton unit 26 can move in the downward direction to diminish theamplitude of the wobble-plate 24 and the stroke of the pump plungers 22.This facility is provided for a brief interval of time following upon asudden decrease in the air induction manifold pressure.

As an alternative to employing the restricted vent passage includingport means 58 and passages 52 and 54, the port means 56 may be utilized.This is brought about as seen in Fig. 3 by arranging for the V-notches72 in the valve 44 to cyclically uncover the port means 56 as the driveshaft 16 is rotated; It is to be understood that in steady-stateoperation of the pump, the valve 44 will assume a position almostclosing the ports 42. For this position of the valve 44 the notches 72and the port means 56 can be proportioned to provide the necessaryrestricted venting. This will not interfere with the increased rate ofventing provided by the port means 56 when they are completely uncovereddue to the valve 44 moving to its extreme upper position. As a furtheralternative a small orifice may be provided in the wall of housingcommunicating with the second pressure chamber therein. This may augmentor replace port means 58.

The invention has been described with reference to a specific embodimentthereof. Nevertheless, it is intended to encompass the numerous changesand modifications which will appear obvious to those skilled in the artto which it appertains, and which come within the scope of the appendedclaims.

What I claim is:

1. A fuel injection pump for internal combustion engines havingadjustable means controlling the stroke of at least one pump member, ahousing, and a displaceable pressure responsive member coupled to saidadjustable means for controlling said adjustable means and disposed insaid housing and forming with said housing a first and a second pressurechamber on respective sides of said member, comprising in combinationtherewith, means communicating withsaid first chamber for supplying asubstantially unrestricted flow of fluid under 6 pressure thereto, aservo-valve-controlled passage inter connecting directly said twochambers, a movable servovalve in valving cooperation with saidcontrolled passage wherein movement of said valve regulatesprogressively the amount of' fluid interconnection between saidchambers, a feedback coupling between said pressure responsive memberand said servo-valve, a restricted passage communicating with saidsecond chamber forventing fluid therefrom to the exterior of saidchambers, the amount of fluid interconnection provided by saidservo-valve and controlled passage being related'in size to the size ofsaid restricted passage for permitting a rapid build-up of pressure insaid second chamber when said servo-valve moves to its valving positionwith respect to said controlled passage corresponding to a fullinterconnection between said chambers, and auxiliary venting meanscommunicating with said second chamber and including a vent passage of asize related to the size of said restricted passage and to the size ofsaid second chamber for rapidly decreasing the pressure in said secondchamber when unobstructed, said servo-valve also being in valvingcooperation with said auxiliary venting means for obstructing the flowof fluid therethrough from said second chamber for all valving positionsof said servo-valve except when said servo-valve is in its valvingposition corresponding to fully obstructing said controlled passage,whereby said displaceable member is rapidly actuated to either of itsextreme positions responsive to movement of said servo-valve to itscorresponding extreme position.

2. A fuel injection pump for internal combustion engines having aplurality of pumping plungers of variable stroke, an adjustablewobble-plate coupled thereto for actuating said plungers, a rotatabledrive shaft, a combined skew shaft and servo-piston unit keyed to andlongitudinally slidable on said drive shaft, said unit being coupled tosaid wobble-plate for altering the amplitude of the motion thereof, anda housing for said combined skew shaft and servo-piston unit formingwith said unit a first and a second pressure chamber on respective sidesof said unit, comprising in combination therewith, means communicatingwith said first chamber for supplying a substantially unrestricted flowof fluid under pressure thereto, a servo-valve-controlled passage havingfirst and second ports in saidfirst and second chambers respectively forinterconnecting said two chambers, a movable servo-valve in valvingcooperation with said second port wherein movement of said valveregulates progressively the amount of opening of said second port, afeedback coupling between said servo-piston unit and said servovalve, arestricted passage communicating with said second chamber for ventingfluid therefrom to the exterior of said pump, the amount of-opening ofsaid second port being related in size to the size of said restrictedpassage for permitting a rapid build-up of pressure in said secondchamber when said servo-valve moves to its valving positioncorresponding to said second port being fully opened, and auxiliaryventing means communicating with said second chamber and including avent passage of a size related to the size of said restricted passageand to the size of said second chamber for rapidly decreasing thepressure in said second chamber when unobstructed, said servo-valve alsobeing in valving cooperation with said auxiliary venting means forobstructing the flow of fluid therethrough from said second chamberexcept when saidservo-valve is in its valving position corresponding tosaid second port being fully closed, whereby said servo-piston unit israpidly actuated to either of its extreme positions responsive tomovement of the servovalve to its corresponding extreme position.

3. A fuel injection pump for internal combustion engines havingapluralityof pumping plungers of variable stroke, an adjustablewobble-plate coupled thereto for actuating said plungers, a rotatabledrive shaft, a combined skew shaft and servo-piston unit keyed to andlongitudinally sl-idable on said drive shaft, said unit being coupled tosaid wobble-plate for altering the amplitude of the motion thereof, andahousing for said combined skew shaft and servo-piston .unit forming withsaid unit a first and a second pressure chamber on respective sides ofsaid unit, comprising in combination therewith, means communicating withsaid first chamber for supplying a substantially unrestricted flow offluid under pressure thereto, a passage formed Within said drive shaftand extending beyond the limits of movement of said servo-piston unit onboth sides thereof, one or more ports formed in the Wall of said driveshaft on each side of said servo'piston unit for establishing directhydraulic communication between said passage and said first and secondchambers, respectively, a servo-valve slidably mounted on said driveshaft within said second chamber for operative valving cooperation withthe drive shaft ports therein, a feedback coupling between saidservo-piston unit and said servo-valve, a permanently open andrestricted passage communicating with said second chamber for ventingthereof, the size of the drive shaft ports in the second chamber beingrelated to the size of said restricted passage for permitting a rapidbuild-up of pressure in said second chamber when the servo-valve is inits wide open valving position with respect to said drive shaft ports,and auxiliary venting means communicating with said second chamber andincluding a vent passage of a size related to the size of saidrestricted passage and to the size of said second chamber for rapidlydecreasing the pressure in said second chamber when unobstructed, saidservo-valve also being in valving cooperation with said auxiliaryventing means for obstructing the flow of fluid therethrough from saidsecond chamber except when said servo-valve is in closed valvingposition with respect to said drive shaft ports of said second chamber,whereby said servo-piston unit is rapidly actuated to either of itslimiting positions responsive to movement of the servo-valve to itscorresponding extreme position.

4. A fuel injection pump according to claim 3, wherein said auxiliaryventing means comprises a second passage within said drive shaftcommunicating at one end with the exterior of said housing and at theother end with further port means in the wall of said shaft whichfurther port means is located within said second chamber with respect tosaid servovalve such that said servovalvecompletely obstructs saidfurther port means for all valving positions of said servo-valve exceptfor the aforesaid servo-valve-closed position.

5. A fuel injection pump for internal combustion engines having aplurality of pumping plungers of variable stroke, an adjustablewobble-plate coupled thereto for actuating said plungers, a rotatabledrive shaft, a combined skew shaft and servo-piston unit keyed to andlongitudinally slidable on said drive shaft, said unit being coupled tosaid wobble-plate for altering the amplitude of the motion thereof, anda housing for said combined skew shaft and servo-piston unit formingwith said unit a first and a second pressure chamber on respective sidesof said unit, comprising in combination therewith, means communicatingwith said first chamber for supplying a substantially unrestricted flowof fluid under pressure thereto, a passage formed within said driveshaft and extending beyond the limits of movement of said servopistonunit on both sides thereof, the wall of said shaft being aperturedwithin said first chamber for establishing communication between saidfirst chamber and said passage, first port means formed in the wall ofsaid drive shaft within said second chamber for establishingcommunication between said passage and said second chamber, aservo-valve in the form of a sleeve member slidably mounted on saiddrive shaft within said second chamber and secured against rotation,said sleeve member having an internal land and groove arrangement forvalving cooperation with said first port means, movement of said sleevemember longitudinally in opposite direction on said shaft functioningrespectively progressively to close and open said first port means, saidfirst port means being substantially completely closed when said sleevemember is at one end of its travel, a feedback coupling between saidservo-piston unit and said sleeve member, an auxiliary passage formed insaid drive shaft communicating at one end with the exterior of saidhousing and at the other end with second port means in the wall of saidshaft disposed within said second chamber, an auxiliary valving surfaceinternally formed on said sleeve member and arranged to cooperate withsaid second port means, said auxiliary valving surface being formed withinterruptions circumferentially disposed therein, which interruptionsintermittently coincide with said second port means as said drive shaftis rotated for intermittently opening said second port means, saidsecond port means being normally sealed by said auxiliary valvingsurface except for said intermittent interruption as long as said sleevemember is away from said one end of its travel, and said second portmeans being fully open when said sleeve member is at said one end of itstravel, said second port means and said interruptions in the auxiliaryvalving surface of said sleeve member being related to the size of saidfirst port means and to the size of said second chamber so as to permita rapid build-up of pressure in said second chamber when the sleevemember moves to substantially fully open said first port means and topermit a rapid decrease in the pressure in said second chamber when thesleeve member is at said one end of its travel, and means coupled tosaid sleeve member for controlling the position thereof whereby saidservo-piston unit is rapidly actuated to either limiting positionresponsive to movement of the sleeve member to its corresponding extremeposition.

6. A fuel injection pump according to claim 5, wherein the interruptionsformed in the surface of said auxiliary valving surface comprise atleast one notch formed in one edge of the sleeve member, and whereinsaid means for controlling the position of the sleeve member comprisesan articulable link engaging said notch for exerting pressure upon saidsleeve member in a longitudinal direction and for simultaneouslyrestraining said sleeve member from rotating.

7. A fuel injection pump for an internal combustion engine of thespark-ignition type having an engine accelerator control, said pumpbeing capable of rapid accommodation to sudden substantial changes inthe position of the engine accelerator control, comprising incombination, a plurality of individual pump members for supplying fuelto the cylinders of said engine, adjustable means coupled to said pumpmembers for controlling the delivery thereof, a displaceable pressureresponsive member cooperating with said adjustable means for controllingsaid adjustable means with movement in one direction causing increasedfuel delivery and movement in the opposite direction causing decreasedfuel delivery, a housing, said displaceable member being disposed insaid housing and forming with said housing a first and a second pressurechamber on respective sides of said member, means communicating withsaid first chamber for supplying a substantially unrestricted fiow offluid under pressure thereto, a servo-valve-controlled passagehydraulically and directly interconnecting said two chambers, a movableservo-valve in valving cooperation with said valve-controlled passagewherein the movement of said servo-valve regulates progressively theamount of hydraulic interconnection between said two chambers, afeedback coupling between said pressure responsive member and saidservo-valve, a restricted passage communicating with said second chamberfor venting thereof, the amount of fluid interconnection provided bysaid servovalve and said valve controlled passage being related in sizeto the size of said restricted passage for permitting a rapid build-upof pressure in said second chamber when said servo-valve is in itsvalving position corresponding to movement of said displaceable memberrapidly in one of said two directions, auxiliary venting meanscommunicating with said second chamber and including a vent pasage of asize related to the size of said restricted passage and to the size ofsaid second chamber for rapidly decreasing the pressure in said secondchamber when unobstructed for moving said displaceable member rapidly inthe other of said two directions, said servo-valve also being in valvingcooperation with said auxiliary venting means for obstructing the flowof fluid therethrough from said second chamber except when saidservo-valve is in a valving position corresponding to obstructing theinterconnection between said first and second chambers, and means forcoupling said servovalve to said engine accelerator control foractuating said servo-valve to its open valving or its closed valvingpositions responsive to sudden substantial changes in the position ofsaid accelerator control in opposite directions respectively, wherebysudden substantial changes in opposite directions in the position of theengine accelerator control will be accompanied by correspondingly rapidincreases and decreases, respectively, in the quantity of fueldelivered.

8. A fuel injection pump for internal combustion engines having aplurality of pumping plungers of variable stroke, an adjustablewobble-plate coupled thereto for actuating said plungers, a rotatabledrive shaft, a combined skew shaft and servo-piston unit keyed to andlongitudinally slidable on said drive shaft, said unit being coupled tosaid wobble-plate for altering the amplitude of the motion thereof, anda housing for said combined skew shaft and servo-piston unitforming withsaid unit a first and a second pressure chamber on respective sides ofsaid unit, comprising in combination therewith means communicating withsaid first chamber for supplying a substantially unrestricted fiow offluid under pressure thereto, a passage formed within said drive shaftand extending beyond the limits of movement of said servopiston unit onboth sides thereof, the wall of said shaft being apertured within saidfirst chamber for establishing communication between said first chamberand said passage, first port means formed in the wall of said driveshaft within said second chamber for establishing communication betweensaid passage and said second chamber, a servo-valve in the form of asleeve member slidably mounted on said drive shaft within said secondchamber and secured against rotation, said sleeve member having aninternal land and groove arrangement for valving cooperation with saidfirst port means, movement of said sleeve member longitudinally inopposite direction on said shaft functioning respectively progressivelyto close and open said first port means, said first port means beingsubstantially completely closed when said sleeve member is at one end ofits travel, a feedback coupling between said servo-piston unit and saidsleeve member, an auxiliary passage formed in said drive shaftcommunicating at one end with the exterior of said housing and at theother end with second port means in the wall of said shaft disposedwithin said second chamber, an auxiliary valving surface internallyformed on said sleeve member and arranged to cooperate with said secondport means, said second port means normally being sealed by saidauxiliary valving surface except when said sleeve member is away fromsaid one end of its travel, and said second port means being fully openwhen said sleeve member is at said one end of its travel, the size ofsaid second port means being related to the size of said first portmeans and to the size of said second chamber so as to permit a rapidbuild-up of pressure in said second chamber when said sleeve membermoves to a valving position substantially fully opening said first portmeans and to permit a rapid decrease in the pressure in said secondchamher when said sleeve member is at said one end of its travel, andmeans coupled to said sleeve member for controlling the position thereofwhereby said servo-piston unit is rapidly actuated to either limitingposition responsive to movements of the sleeve member to itscorresponding extreme position.

References Cited in the file of this patent UNITED STATES PATENTS2,439,498 Wallace Apr. 13, 1948 2,448,347 Beeh Aug. 31, 1948 2,611,318Wahlmark Sept. 23, 1952 2,624,326 Fiser Jan. 6, 1953 2,667,840 High Feb.2, 1954 2,672,816 Friedlander Mar. 23, 1954

